The present invention relates to a vacuum switch including vacuum-measurement devices, switchgear using the vacuum switch, and an operation method thereof.
The break performance and the withstand-voltage performance of a vacuum switchgear rapidly deteriorate when the degree of vacuum decreases to below 10xe2x88x924 Torr. Changes in the degree of vacuum are caused by leakage-in of gas from cracks which have chapped, discharge of gas molecules which have been absorbed in metal and insulation members composing a vacuum vessel, penetration of ambient gas, etc. As the size of a vacuum vessel is increased in accordance with an increase of the applied voltage, it becomes unable to disregard the penetration of ambient gas into the vacuum vessel. It is well known that the degree of vacuum in a vacuum circuit-breaker is monitored by various means. For example, such monitoring methods or apparatuses are disclosed in U.S. Pat. No. 5,537,858, U.S. Pat. No. 5,739,419, U.S. Pat. No. 4,163,130, Japanese Utility Model Application Laid-Open Sho.55-45160, Japanese Patent Application Laid-Open Sho.56-36818, Japanese Patent Application Laid-Open Hei.8-306279, etc. In the contact-type measurement method such as that disclosed in U.S. Pat. No. 4,163,130, of measuring the degree of vacuum in a vacuum vessel which is not grounded, in order to elevate the voltage of a vacuum-measurement device, which is equal to the voltage of a main circuit, from the ground voltage, a transformer is necessary, and has not come into practical use yet.
Further, although the non-contact-type vacuum-measurement methods for a vacuum vessel are devised in U.S. Pat. No. 5,537,858, Hei.8-306279, etc., a method of measuring changes in the degree of vacuum in a vacuum vessel with the required accuracy has not become known yet. In Japanese Utility Model Application Laid-Open Sho.55-45160, although it is not described that the vacuum vessel is grounded, the system in which a vacuum-measurement device attached to a second vacuum vessel containing a first vacuum vessel is disclosed. Further, it is described in this Japanese Utility Model Application Laid-Open, that a vacuum pump beside a vacuum-measurement device is connected to the second vacuum vessel. However, since the first vacuum vessel does not communicate with the second vacuum vessel, the degree of vacuum in the first vacuum vessel cannot be directly measured.
If a vacuum sensor is separated from a main circuit by using an insulation member, the size of the vacuum sensor, including the insulation member, is mostly as large as a vacuum valve. Further, there is a problem in that since electrons generated in the sensor, then generate secondary electrons while colliding with the insulation member, that is, they cause electron multiplication, and these electrons further enter the vacuum valve, the insulation characteristics of the vacuum valve deteriorates. By setting the potential of a line connected to a power source equal to that of an outer cylindrical electrode of the vacuum sensor element, and applying the voltage, divided by a capacitor, to an inner cylindrical electrode, it is possible to remove the insulation member, which in turn downsizes the vacuum sensor. However, the size of a vacuum measurement device becomes large in the last results because insulation of the capacitor from the earth is necessary, and the vacuum measurement device is apt to receive influences of changes in the voltage of the main circuit (for example, surge voltage). Further, since the potential of the vacuum sensor element is equal to that of the line connected to the power source, an insulation transformer or a light transmission line is necessary to transmit a signal to a measurement unit, an alarm lamp, a relay for generating an alarm, etc., and this makes the measurement system complicated.
An objective of the present invention is to provide a vacuum switch and a vacuum switchgear using the vacuum switch, in which the vacuum switch is downsized, and its degree of vacuum can be measured and monitored reliably, by putting a vacuum circuit-breaker and a disconnector into different grounded vacuum vessels, respectively, by providing a vacuum measurement device at each grounded vessel; and its reliability is improved by composing the vacuum switchgear so that, even if a defect or a malfunction occurs in the vacuum circuit-breaker and the disconnector, its effects do not propagate in the whole of the vacuum switch.
To achieve the above objective, the present invention provides a vacuum switch comprising: grounded vacuum vessels in which a vacuum circuit-breaker portion and a disconnector portion are contained respectively; and vacuum-measurement devices which are attached to the grounded vacuum vessels, respectively.
In the present invention, the vacuum circuit-breaker portion includes indispensable components composing this circuit breaker, that is: movable and fixed electrodes, conductors supporting these electrodes, and a vessel containing these components. Further, the disconnector portion is an apparatus, connected to the circuit-breaker, for maintaining the circuit-breaker in a disconnection state when it is required, and it sometimes includes a grounding switch. Furthermore, it includes a vessel containing these components.
Further, it is desirable in order to assure the safety of workers who inspect and maintain loads or a switchgear, to provide a function for checking or continuously monitoring the degree of vacuum in an operation unit, at a structure of a switchgear according to the present invention, in which a circuit-breaker, a disconnector, and a grounding switch are integrated in a vacuum vessel. As a vacuum valve including a vacuum-measurement device, a vacuum valve using an ionization vacuum gauge, a detector to detect the degree of vacuum by applying voltage to a small gap provided in a vacuum vessel to cause discharge in the gap, or a magnetron-type vacuum-sensing element, are well known. Although all the above well-known detectors can be used in the present invention, it is favorable to use an ionization vacuum gauge or a magnetron-type vacuum-sensing element from the view point of reliability and accuracy. Also, it is possible to adopt the composition in which a megger is connected to a measurement element, although this composition is not suitable for continuous monitoring of the degree of vacuum. By using this composition, the degree of vacuum can be measured without a specific power source.
In the vacuum switch of the present invention, a fixed electrode and a movable electrode are arranged opposite to each other in the vacuum vessel from which these electrodes are insulated with insulation members, and a first vacuum vessel surrounding this vacuum vessel is provided. Further, a vacuum-measurement device is attached to the first vacuum vessel. Further, it is possible that when the degree of vacuum is measured, a set of coaxial electrodes and a magnetic field-generation unit surrounding the coaxial electrodes is attached to the first vacuum vessel which is grounded and in which the fixed electrode and the movable electrode are arranged opposite to each other; and when the degree of vacuum is not measured, the set is detached from the first vacuum vessel. Furthermore, it is desirable to provide a vacuum pump at the grounded vacuum vessel in order to recover the degree of vacuum in this vacuum vessel when the vacuum deteriorates.
In accordance with the vacuum switchgear of the present invention, since the vacuum-sensing element can be electrically separated from the main circuit, the reliability of the function for measuring or monitoring the degree of vacuum can be improved, and if the degree of vacuum deteriorates, the vacuum can be recovered by the vacuum pump, which in turn ensures the safety of the switchgear. Also, by separating the circuit-breaker portion from the disconnector portion, it is possible to prevent a malfunction which has occurred in either the circuit-breaker portion or the disconnector portion, from propagating in the whole of the switchgear. Moreover, since the degree of vacuum in the vacuum vessel containing the circuit-breaker portion can be directly monitored, the reliability of the circuit-breaker portion is improved.
Since the pair of the movable and the fixed electrodes in the circuit-breaker portion is coaxially arranged with the pair of the movable and the fixed electrodes in the disconnector portion, even if a large driving force is applied to these pairs of electrodes in a disconnecting operation, this driving force can be absorbed or alleviated by those coaxially arranged components, which in turn can improve the reliability of the vacuum switch. Further, since the vacuum vessel is surrounded by the first or second grounded vacuum vessel, even if a malfunction occurs in the vacuum vessel, the vacuum vessel can be protected from the malfunction by the first or second grounded vacuum vessel.
In accordance with the vacuum switch and the operation method of the switchgear according to the present invention, by operating the vacuum pump as the occasion arises, or at will, the degree of vacuum in not only the grounded vacuum vessels, but also the vacuum vessel containing the vacuum circuit-breaker, is improved or maintained at a necessary level, and this can remarkably improve the performances of the vacuum switch and the vacuum switchgear. switch and vacuum switchgear using the vacuum switch.